Oxidation method and oxidation system

ABSTRACT

An oxidation method is capable of forming oxide films in an improved interfilm thickness uniformity. The oxidation method includes the steps of supplying an oxidizing gas and a reducing gas into a processing vessel  22  capable of being evacuated and holding a plurality of workpieces W arranged at predetermined pitches, and creating a process atmosphere containing active oxygen species and active hydroxyl species in the processing vessel  22  through the interaction of the oxidizing gas-and the reducing gas. At least either of the oxidizing gas and the reducing gas is jetted into an upstream region S 1 , a middle region S 2  and a downstream region S 3 , with respect to the flowing direction of the gas, of a processing space S containing the workpieces W.

CROSS REFERENCE TO RELATED APPLICATION

This application is a division of Ser. No. 10/992,469, filed Nov. 19,2004, now U.S. Pat. No. 7,129,186 which is being incorporated in itsentirety herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an oxidation method of oxidizing thesurface of a workpiece, such as a semiconductor wafer, and an oxidationsystem for carrying out the oxidation method.

2. Description of the Related Art

Generally, a semiconductor integrated circuit if fabricated bysubjecting a semiconductor wafer, such as a silicon wafer, to processesincluding a film deposition process, an etching process, an oxidationprocess, a diffusion process and a modifying process. The oxidationprocess, for example, oxidizes the surface of a single-crystal orpolycrystalline silicon film or a metal film. The oxidation process isused particularly for forming a gate oxide film and an insulating filmfor a capacitor.

Oxidation processes are classified into atmospheric oxidation processesto be carried out in an atmosphere of a pressure approximately equal tothe atmospheric pressure in a processing vessel and low=-pressureoxidation processes to be carried out in a vacuum atmosphere in aprocessing vessel evacuated at a vacuum in terms of process pressure orinto wet oxidation processes using, for example, steam generated byburning hydrogen by an external combustion apparatus, such as a wetoxidation process disclosed in Patent document 1, and dry oxidationprocesses not using steam and supplying only ozone or oxygen into aprocessing vessel, such as a dry oxidation process disclosed in Patentdocument 2.

Generally, insulating films formed by the wet oxidation process aresuperior to those formed by the dry oxidation process in terms ofcharacteristics including compressive strength, corrosion resistance andreliability. Generally, the atmospheric wet oxidation process is able toform the insulating film at an oxidation rate higher than that at whichthe low-pressure wet oxidation process. However, the insulating filmformed by the atmospheric wet oxidation process is inferior to thatformed by the low-pressure wet oxidation process in thicknessuniformity.

Conventional design rules for semiconductor integrated circuits are notvery severe and hence the foregoing various oxidation processes havebeen used properly taking into consideration purposes of oxide films,process conditions and equipment cost. Recently, semiconductorintegrated circuits need very narrow lines and very thin films, andsevere design rules must be applied to designing semiconductorintegrated circuits. Consequently, films having higher quality, highercharacteristics and higher thickness uniformity have been required inrecent years. The conventional oxidation processes are unable to copewith such high requirements.

An oxidation system disclosed, for example, in Patent document 3 carriesout a wet oxidation process by supplying hydrogen gas (H₂) and oxygengas (O₂) separately into a space at the lower end of a vertical quartzreaction tube, generating steam through the interaction of H₂ and O₂ ina combustion space formed in a quartz cap, and supplying the steamupward toward wafers to oxidize the wafers. Since H₂ is burned in thecombustion space, the atmosphere in a downstream part of the space inthe processing vessel has a high steam concentration and the atmospherein an upper part of the space in the processing vessel has a low steamconcentration because the steam is consumed as the same flows upward inthe processing vessel. Consequently, in some cases, the thickness of anoxide film formed on the wafer is dependent on the position of the waferin the processing vessel and oxide films of different thicknesses areformed on the wafers, respectively.

A batch-type oxidation system disclosed in Patent document 4 arranges aplurality of semiconductor wafers in a horizontal reaction tube andsupplies O₂ from one end of the reaction tube into the reaction tube orsupplies O₂ and H₂ simultaneously into the reaction tube to form oxidefilms on the semiconductor wafers in a low-pressure atmosphere. Thisoxidation system forms a film in an atmosphere of a comparatively highpressure by a hydrogen-burning oxidation process. Since steam is aprincipal element of reaction in this oxidation system, it is possiblethat the difference in steam concentration between an upstream part anda downstream part of the space in the processing vessel with respect tothe flowing direction of the gas is excessively large and oxide filmshaving different thicknesses are formed on the semiconductor wafers.

A single-wafer processing oxidation system disclosed in Patent document5 supplies oxygen gas and hydrogen gas into a processing vessel,generates steam in the vicinity of a semiconductor wafer, such as asilicon wafer, held in the processing vessel through the interaction ofthe oxygen gas and the hydrogen gas to form an oxide film by oxidizingthe surface of the semiconductor wafer. When this single-waferprocessing oxidation system is used, oxygen gas and hydrogen gas aresupplied into the processing vessel through gas inlets at a shortdistance between 20 and 30 mm from the semiconductor wafer to generatesteam in the vicinity of the surface of the semiconductor wafer throughthe interaction of the oxygen gas and the hydrogen gas, and acomparatively high process pressure is used. Consequently, the oxidefilm thus formed on the semiconductor wafer is unsatisfactory inthickness uniformity.

The applicant of the present invention patent application disclosed anoxidation method in Patent document 6. This oxidation method supplies anoxidizing gas, such as oxygen gas, and a reducing gas, such as hydrogengas, simultaneously into an upstream part and a downstream part,respectively, of a processing chamber, makes the oxidizing gas and thereducing gas interact in a vacuum atmosphere to create an atmospherecontaining, as principal elements, active oxygen species and activehydroxyl species, and oxidizes a silicon wafer or the like in thisatmosphere.

The oxidation method disclosed in Patent document 6 will be brieflyexplained with reference to FIG. 4 showing a conventional oxidationsystem 2. The oxidation system 2 has a cylindrical, vertical processingvessel 6 and a resistance heater 4 surrounding the processing vessel 6.A wafer boat 8 is loaded into and unloaded from the processing vessel 6through the lower open end of the processing vessel 6 by a wafer boatlifter. The wafer boat 8 holds semiconductor wafers W, such as siliconwafers, in a vertical arrangement. A H₂ supply nozzle 10 for supplyingH₂ and an O₂ supply nozzle 12 for supplying O₂ are connected to lowerparts of the side wall of the processing vessel 6. A discharge port 14formed in the upper wall of the processing vessel 6 is connected to avacuum pump or the like.

Hydrogen gas and oxygen gas supplied through the supply nozzles 10 and12 into a lower part of a process chamber in the processing vessel 6interact in the processing chamber at a pressure below 133 Pa in theprocessing vessel 6 to generate active oxygen species and activehydroxyl species. Those active species come into contact with thesurfaces of the wafers W as the same rise in the processing vessel 6 tooxidize the surfaces of the wafers W.

Patent document 1: JP-A 3-140453

Patent document 2: JP-A 57-1232

Patent document 3: JP-A 4-18727

Patent document 4: JP-A 57-1232

Patent document 5: U.S. Pat. No. 6,037,273

Patent document 6: JP-B 2002-176052

Oxidation methods disclosed in Patent documents 1 to 6 are capable offorming oxide films of a satisfactory quality in high intrafilmthickness uniformity. However, those oxide films are unsatisfactory ininterfilm thickness uniformity. It is inferred that such unsatisfactoryinterfilm thickness uniformity is due to a high active speciesconcentration in an upstream part of the processing chamber with respectto the flowing direction of the gases and a low active speciesconcentration in a downstream part of the processing chamber. Earlysolution of problems that may arise due to such unsatisfactory interfilmthickness uniformity is desired in these days when the severity ofdesign rules for semiconductor devices and the reduction of line widthfilm thickness are progressively increasing.

It may be possible to form films in satisfactory interfilm thicknessuniformity by heating the wafers held on the wafer boat at differenttemperatures gradually changing in the direction of arrangement of thewafers by the so-called temperature tilt control. Since the respectivetemperatures of the wafers held on the wafer boat differ slightly fromeach other, the different wafers have different heat histories,respectively, and the different heat histories may affect adversely tothe characteristics of the films. Accordingly, temperature tilt controlis unacceptable.

SUMMARY OF THE INVENTION

The present invention has been made in view of those problems to solvethose problems effectively. Accordingly, it is an object of the presentinvention to provide an oxidation method capable of forming oxide filmsin improved interfilm thickness uniformity and an oxidation system forcarrying out the oxidation method.

An oxidation method in a first aspect of the present invention includesthe steps of: supplying an oxidizing gas and a reducing gas into aprocessing vessel defining a processing space, and capable of holding aplurality of workpieces at predetermined pitches and of being evacuated;creating a process atmosphere containing active oxygen species andactive hydroxyl species through the interaction of the oxidizing gas andthe reducing gas; and oxidizing surfaces of the workpieces in theprocess atmosphere; wherein at least either of the oxidizing gas and thereducing gas is jetted into an upstream region, a middle region and adownstream region of the processing space where the workpieces are held.

For example, in the oxidation method, the oxidizing gas is jetted onlyinto the upstream region, with respect to the flowing direction of thegas, of the processing space.

The oxidizing gas contains at least one of O₂, N₂O, NO, NO₂ and O₃, andthe reducing gas contains at least one of H₂, NH₃, CH₄, HCl and heavyhydrogen.

A recording medium in a second aspect of the present invention storescontrol software for controlling an oxidation system to carry out anoxidation method of oxidizing surfaces of a plurality of workpiecesarranged at predetermined pitches in a processing vessel capable ofbeing evacuated including the steps of: jetting an oxidizing gas and areducing gas into the processing vessel, creating a process atmospherecontaining active oxygen species and active hydroxyl species through theinteraction of the oxidizing gas and the reducing gas, and oxidizingsurfaces of the workpieces in the process atmosphere; wherein the stepof jetting the oxidizing gas and the reducing gas into the processingvessel jets at least either of the oxidizing gas and the reducing gasinto an upstream region, a middle region and a downstream region, withrespect to the flowing direction of the gases, of a processing spacedefined by the processing vessel.

For example, the step of jetting the gases jets the oxidizing gas onlyinto the upstream region, with respect to the flowing direction of thegases, of the processing space.

For example, the oxidizing gas contains at least one of O₂, N₂O, NO, NO₂and O₃, and the reducing gas contains at least one of H₂, NH₃, CH₄, HCland heavy hydrogen.

An oxidation system in a third aspect of the present invention includes:a workpiece holding means for holding a plurality of workpieces atpredetermined pitches; a processing vessel of a predetermined lengthcapable of containing the workpiece holding means to subject theworkpieces to an oxidation process and of being evacuated; a heatingmeans for heating the workpieces; an evacuating system for evacuatingthe processing vessel; an oxidizing gas supply means for supplying anoxidizing gas into the processing vessel; and a reducing gas supplymeans for supplying a reducing gas into the processing vessel; whereinat least either of the oxidizing gas supply means and the reducing gassupply means includes gas outlets opening at least into an upstreamregion, a middle region and a downstream region, with respect to theflowing direction of the gas, of a processing space in the processingvessel in which the workpieces are arranged.

For example, in the oxidation system, the oxidizing gas supply means hasan oxidizing gas jetting nozzle having only a single gas outlet openinginto the upstream region, with respect to the flowing direction of thegas, of the processing space.

For example, in the oxidation system, the reducing gas supply means hasat least one reducing gas jetting nozzle extended along the processingspace and provided with at least gas outlets opening into the upstreamregion, the middle region and the downstream region, with respect to theflowing direction of the gas, of the processing space.

For example, in the oxidation system, the reducing gas supply means hasa first reducing gas jetting nozzle having a gas outlet opening into theupstream region, with respect to the flowing direction of the gas, ofthe processing space and a second reducing gas jetting nozzle having gasoutlets respectively opening into the middle and the downstream region.

For example, in the oxidation system, the reducing gas supply means hasa reducing gas jetting nozzle provided with a plurality of gas outletsarranged at predetermined pitches over all the length of the processingspace.

For example, in the oxidation system, the reducing gas supply means hasa reducing gas jetting nozzle having an up section extending from theupstream to the downstream region of the processing space, a bend formedby bending the reducing gas nozzle in the downstream region, and a downsection extending down from the bend to the upstream region and providedwith a plurality of gas outlets longitudinally arrangement atpredetermined pitches.

For example, in the oxidation system, the reducing gas supply means hasa first reducing gas jetting nozzle extended substantially over all theprocessing space and provided with a plurality of gas outlets formed atpredetermined pitches, and a second reducing gas jetting nozzle havingan up section extending from the upstream to the downstream region ofthe processing space, a bend formed by bending the reducing gas nozzlein the downstream region, and a down section extending down from thebend to the upstream region and provided with a plurality of gas outletslongitudinally arrangement at predetermined pitches.

For example, in the oxidation system, the reducing gas supply means hasa reducing gas jetting nozzle provided with gas outlets only in asection thereof extending in the upstream region of the processingspace.

For example, in the oxidation system, the oxidizing gas supply means hasat least one oxidizing gas jetting nozzle extending in the processingspace and provided with gas outlets opening into the upstream, themiddle and the down stream region, with respect to the flowing directionof the gas, of the processing space.

The oxidizing gas contains at least one of O₂, N₂O, NO, NO₂ and O₃, andthe reducing gas contains at least one of H₂, NH₃, CH₄, HCl and heavyhydrogen.

According to the present invention, at least either of the oxidizing gasand the reducing gas is jetted into the upstream, the middle and thedownstream region of the processing space to improve the interfilmthickness uniformity of the oxide films.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of an oxidation system in a first embodimentaccording to the present invention;

FIGS. 2(A) to 2(E) are typical views of different gas jetting nozzlearrangements;

FIG. 3 is a graph comparatively showing respective thicknesses of SiO₂films (oxide films) formed on wafers disposed respectively at differentpositions by an oxidation system in a second embodiment according to thepresent invention and the respective thicknesses of SiO₂ films formed onwafers disposed respectively at different positions by a conventionaloxidation system; and

FIG. 4 is a schematic view of a conventional oxidation system.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

An oxidation method and oxidation systems embodying the presentinvention will be described with reference to the accompanying drawings.

An oxidation system 20 in a first embodiment according to the presentinvention for carrying out an oxidation method according to the presentinvention will be described with reference to FIG. 1. The oxidationsystem 20 includes a vertical, cylindrical processing vessel 22 havingan open lower end. The processing vessel 22 may be formed of, forexample, quartz having high heat resistance.

A discharge port 24 is formed in the top wall of the processing vessel22. A horizontal discharge line 26 has a vertical part connected to thedischarge port 24. An evacuating system 32 including a pressure controlvalve 28 and a vacuum pump 30 is connected to the discharge line 26 toevacuate the processing vessel 22.

A cylindrical manifold 34 formed of, for example, a stainless steel isdisposed under the processing vessel 22 to support the processing vessel22 thereon. A quartz wafer boat 36 holds a plurality of semiconductorwafers W (hereinafter, referred to simply as “wafers W”), namely,workpieces, in a vertical arrangement at predetermined pitches. Thewafer boat 36 can be vertically moved to load the wafers W into andunload the same from the processing vessel 22 through the open lower endof the processing vessel 22. A sealing member, such as an O ring, isheld between the lower end of the processing vessel 22 and the upper endof the manifold 34 to seal the joint of the processing vessel 22 and themanifold 34. The wafer boat 36 is able to hold, for example, about fifty300 mm diameter wafers W in a vertical arrangement at substantiallyequal pitches.

The wafer boat 36 is supported on a quartz heat-insulating tube 40mounted on a table 42. The table 42 is joined to the upper end of arotating shaft 46 penetrating a lid 44 for covering the lower open endof the manifold 34. A gap between the rotating shaft 46 and the lid 44is sealed by a magnetic fluid seal 48 to create a nonleaking unionbetween the rotating shaft 46 and the lid 44 when the rotating shaft 46rotates. A sealing member 50, such as an O ring, is held between aperipheral part of the lid 44 and the lower end of the manifold 34 toseal the processing vessel 22 in an airtight fashion.

The rotating shaft 46 is supported on a free end of an arm 54 supportedon a lifting mechanism 52, such as a boat elevator. The wafer boat 36and the lid 44 can be simultaneously moved in vertical directions. Thetable 42 may be fixed to the lid 44 to process the wafers W withoutrotating the wafer boat 36.

The processing vessel 22 is surrounded by a heating unit 56 similar tothat mentioned in JP-A 2003-209063. The heating unit 56 is provided witha heating element formed from a carbon wire. The heating unit 56 heatsthe processing vessel 22 and the wafers W held in the processing vessel22. The heating element formed from a carbon wire is capable of keepinga process environment clean and has an excellent temperature elevatingand lowering characteristic. The heating unit 56 is covered with aheat-insulator 58 to ensure thermal stability. Gas supply members forsupplying gases into the processing vessel 22 are arranged on themanifold 34.

More concretely, an oxidizing gas supply system 60 for supplying anoxidizing gas into the processing vessel 22 and a reducing gas supplysystem 62 for supplying a reducing gas into the processing vessel 22 areconnected to the manifold 34. The oxidizing gas supply system 60 and thereducing gas supply system 62 have an oxidizing gas jetting nozzle 64and a reducing gas jetting nozzle 66 respectively. The gas jettingnozzles 64 and 66 penetrate the side wall of the manifold. Gas supplylines 68 and 70 are connected to the gas jetting nozzles 64 and 66respectively. Flow controllers 72 and 74, such as mass flow controllers,are placed in the gas supply lines 68 and 70, respectively. The flow ofgases through the gas supply lines 68 and 70 is controlled by the flowcontrollers 72 and 74 by a main controller 76, such as a microcomputer.The main controller 76 controls all the operations of the oxidationsystem 20. The main controller 76 is provided with a recording medium77, such as a floppy disk. Control software (control program) forcontrolling the oxidation system 20 to carry out an oxidation methodaccording to the present invention is stored in the recording medium 77.

At least either of the oxidizing gas supply system 60 and the reducinggas supply system 62 has gas outlets opening into an upstream region, amiddle region and a downstream region of a processing space S in theprocessing vessel 22.

The wafers W are held in the processing space S in the processing vessel22. Gases supplied into the processing vessel 22 flow upward in theprocessing space S and are discharged through the discharge port 24formed in the top wall of the processing vessel 22. The height of theprocessing space S is slightly greater than that of the wafer boat 36.The processing space S is divided into an upstream region S1, namely, alower region as viewed in FIG. 1, a middle region S2, namely, a middleregion as viewed in FIG. 1, and a downstream region S3, namely, an upperregion as viewed in FIG. 1, for convenience.

In the oxidation system 20 in the first embodiment, the oxidizing gassupply system 60 has the single oxidizing gas jetting nozzle 64 having agas outlet 64A opening into the upstream region S1. More specifically,the gas outlet 64A is disposed at a level at a distance below the levelof the lower end of the wafer boat 36 loaded into the processing vessel22. The oxidizing gas jetting nozzle 64 may be either straight to jetthe oxidizing gas in a horizontal direction or bent in an L-shape to jetthe oxidizing gas upward.

The reducing gas supply system 62 has the single reducing gas jettingnozzle 66. The reducing gas jetting nozzle 66 is extended verticallyover the processing space S. The reducing gas jetting nozzle 66 isprovided with gas outlets 66A longitudinally arranged at predeterminedpitches. Thus the reducing gas jetting nozzle 66 is able to jet thereducing gas horizontally into all the regions of the processing spaceS, namely, the upstream region S1, the middle region S2 and thedownstream region S3. A nozzle provided with a plurality of gas outletslike the reducing gas jetting nozzle 66 will be called also “dispersionnozzle”. The reducing gas jetting nozzle 66 may be provided with a gasoutlet at its upper end to jet the reducing gas upward. The oxidationsystem 20 may be provided with a plurality of reducing gas jettingnozzles to supply the reducing gas over the entire processing space S,which will be described in connection with an oxidizing system inanother embodiment according to the present invention.

The nozzles, 64 and 66 have an inside diameter between about 1 and about4 mm. The pitches of the gas outlets 66 a are in the range of abut 10and about 20 mm. For example the pitches of the gas outlets 66A may besubstantially equal to the pitches of the wafers W on the wafer boat 36.The number of the gas outlets 66A is between 15 and 25. In thisembodiment, the oxidizing gas is O₂ and the reducing gas is H₂. Whennecessary, the oxidation system 20 is provided with an inert gas supplysystem, not shown, for supplying an inert gas, such as N₂.

An oxidation method to be carried out by the oxidation system 20 will bedescribed.

When the oxidation system 20 is in a waiting condition where wafers W,such as silicon wafers, are not loaded into the processing vessel 22,the processing vessel 22 is maintained at a temperature lower than aprocess temperature. The wafer boat 36 holding a plurality of wafers W,such as fifty wafers W, is lifted up from below the processing vessel 22in the state of a hot wall and is loaded into the processing vessel 22.Then, the lid 44 is joined to the open lower end of the manifold 34 toseal the processing vessel 22.

Then, the processing vessel 22 is evacuated and the internal pressure ofthe processing vessel 22 is maintained at a predetermined processpressure, and power supplied to the heating unit 56 is increased to heatthe wafers W at a process temperature for oxidation. After thetemperature of the wafers W has stabilized at the process temperature,predetermined process gases, namely, O₂ and H₂ in this embodiment, aresupplied at controlled flow rates through the oxidizing gas jettingnozzle 64 and the reducing gas jetting nozzle 66 of the gas supplysystems 60 and 62, respectively, into the processing vessel 22.

The oxidizing gas and the reducing gas interact in an evacuatedatmosphere as the same flow upward in the processing vessel 22 togenerate active oxygen species and active hydroxyl species. The activespecies come into contact with the surfaces of the wafers W held on thewafer boat 36 to oxidize the surfaces of the wafers W. The process gasesor gases produced by reaction are discharged through the discharge port24 formed in the top wall of the processing vessel 22 from the oxidationsystem 20.

Hydrogen gas is supplied at a flow rate between 200 and 5,000 sccm, forexample, at 600 sccm. Oxygen gas is supplied at a flow rate between 200and 10,000 sccm, for example, 1,200 sccm.

As O₂ and H₂ separately supplied into the processing vessel 22 flowupward in the processing vessel 22 in the state of a hot wall. Thehydrogen gas burns in the vicinity of the wafers W to create an activeatmosphere mainly of active oxygen species O* and active hydroxylspecies OH*. The active species oxidize the surface of the wafers W toform SiO₂ films. Process conditions include a wafer temperature between400 and 1,000° C., for example, 900° C., a process pressure between 13.3and 1,330 Pa, for example, 133 Pa (1 torr) and a processing time of, forexample, 10 min.

It is inferred that H₂ burns in the vicinity of the wafers W byreactions represented by chemical formulas shown below when O₂ and H₂are supplied separately into the evacuated processing vessel 22 in thestate of a hot wall. In the chemical formulas shown below, chemicalnotations with an asterisk are active species.H₂+O₂→H*+HO₂O₂+H*→OH*+O*H₂+O*→H*+OH*H₂+OH*→H*+H₂O

When O₂ and H₂ are supplied separately into the processing vessel 22,active oxygen species O*, active hydroxyl species OH* and steam H₂O aregenerated during the burning reaction of H₂ and the surfaces of thewafers W are oxidized by those active species to form SiO₂ films. It isinferred that the active oxygen species O* and the active hydroxylspecies OH* contribute effectively to oxidation. Since the reducing gasjetting nozzle 66 is a dispersion nozzle provided with thelongitudinally arranged gas outlets 66A, the hydrogen gas is distributedover the entire processing space S, namely, over the upstream region S1,the middle region S2 and the downstream region S3. The oxygen gasflowing upward from the bottom of the processing space S reacts with thehydrogen gas gradually to generate the active oxygen species and theactive hydroxyl species. Therefore, all the wafers W at different levelsin the processing space S are surrounded by an atmosphere properlycontaining the active species and having a uniform speciesconcentration. Consequently, the oxide films are formed in an improvedinterfilm thickness uniformity.

An experimental oxidation process was performed. The interfilm thicknessuniformity was ±2.89% which was far higher than an interfilm thicknessuniformity of ±5.41% achieved by the conventional oxidation system shownin FIG. 4. Oxide films formed on the wafers W at different positions hadsatisfactorily high intrafilm thickness uniformities in the range of±0.65% to ±0.78%, respectively.

The oxidation system 20 in the first embodiment may employ a diffusionnozzle as the oxidizing gas jetting nozzle 64 for supplying O₂. However,since oxygen concentration, as compared with hydrogen concentration, isdistributed comparatively uniformly in the processing space S, theoxidizing gas jetting nozzle 64 does not need to be a diffusion nozzle.

Effects of oxidizing gas jetting nozzles 64 of different types andreducing gas jetting nozzles 66 of different types were examined.Results of examination will be explained in connection with FIG. 2.

FIGS. 2(A) to 2(E) are typical views of different gas jetting nozzlearrangements. Oxidation systems respectively provided with the gasjetting nozzle arrangements shown in FIGS. 2(A) to 2(E) were operatedunder the process conditions, namely, the process temperature, theprocess pressure and the flow rates of gases, mentioned in connectionwith the description of the oxidation system 20 shown in FIG. 1.

FIG. 2(A) is a typical view of the oxidation system 20 shown in FIG. 1.Films formed by the oxidation system shown in FIG. 2(A) had an interfilmthickness uniformity of ±2.89%.

FIG. 2(B) is a typical view of an oxidation system in a secondembodiment according to the present invention. The oxidation system inthe second embodiment is provided with an oxidizing gas jetting nozzle80 similar to the oxidizing gas jetting nozzle 64 of the oxidationsystem in the first embodiment shown in FIG. 2(A) and two reducing gasjetting nozzles, namely, a first reducing gas jetting nozzle 82 and asecond reducing gas jetting nozzle 84. The first reducing gas jettingnozzle 82 is similar in construction to the oxidizing gas jetting nozzle80. The first reducing gas jetting nozzle 82 has a gas outlet 82Aopening into the upstream region S1. The second reducing gas jettingnozzle 84 is similar in length and construction to the reducing gasjetting nozzle 66 of the oxidizing system 20 in the first embodimentshown in FIG. 2(A). The second reducing gas jetting nozzle 84 isprovided with three gas outlets 84A respectively opening into the middleregion S2, a lower part of the downstream region S3 and an upper part ofthe downstream region S3 to jet the reducing gas in a horizontaldirection. The top gas outlet 84A may open upward to jet the reducinggas upward.

The gas outlets 82A and 84A of the reducing gas jetting nozzles 82 and84 correspond respectively to the upstream region S1, the middle regionS2 and the downstream region S3. The gas outlet 84A corresponding to thedownstream region S3 may be formed in the upper end of the secondreducing gas jetting nozzle 84 to jet H₂ upward. A position P1 in FIG. 3corresponds to a level P1 in FIG. 2(B).

In the second embodiment, the gas outlets 84A of the second reducing gasjetting nozzle 84 are localized as compared with the gas outlets 66A ofthe reducing gas jetting nozzle 66 of the first embodiment shown in FIG.2(A). Since the mass of H₂ is very small, H₂ diffuses at a very highdiffusion rate. Therefore, H₂ gas jetted through the localized gasoutlets 84A of the second reducing gas jetting nozzle 84 and through thegas outlet 82A of the first reducing gas jetting nozzle 82 diffuses allover the processing space S. Films formed by the oxidation system in thesecond embodiment had a very high interfilm thickness uniformity of±0.9%. The films had high intrafilm thickness uniformities within ±1%.

Results of oxidizing processes carried out by the oxidizing system inthe second embodiment and the conventional oxidizing system will becomparatively explained with reference to FIG. 3. FIG. 3 is a graphcomparatively showing the thicknesses of SiO₂ films (oxide films) formedon fifty wafers by the oxidation system in the second embodiment andthose of SiO₂ film formed on fifty wafers by the conventional oxidationsystem. As obvious from FIG. 3, whereas the SiO₂ films formed by theconventional oxidation system on the wafers at different levels havewidely different thicknesses, the SiO₂ films formed by the oxidationsystem in the second embodiment on the wafers at different levels,respectively, are distributed within a narrow range in a high interfilmthickness uniformity.

FIG. 2(C) is a typical view of an oxidation system in a third embodimentaccording to the present invention. The oxidation system in the thirdembodiment is provided with an oxidizing gas jetting nozzle 86 similarto the oxidizing gas jetting nozzle 64 of the oxidation system in thefirst embodiment shown in FIG. 2(A) and a reducing gas jetting nozzle88. The reducing gas jetting nozzle 88 has an up section extending fromthe upstream region S1 to the downstream region S3 of the processingspace S, a bend formed by bending the reducing gas nozzle in thedownstream region S3, and a down section extending down from the bend tothe upstream region S1. The down section of the reducing gas jettingnozzle 88 is provided with a plurality of gas outlets 88A longitudinallyarrangement at predetermined pitches similarly to the gas outlets 66A ofthe reducing gas jetting nozzle 66 shown in FIG. 2(A). Hydrogen gas isjetted horizontally through the gas outlets 88A all over the processingspace S. Hydrogen gas flowing through the long reducing gas jettingnozzle 88 is preheated, which promotes the reaction of hydrogen gas withoxygen gas. Films formed by the oxidation system in the third embodimenthad a high interfilm thickness uniformity of ±1.5%. The films hadsatisfactory intrafilm thickness uniformities within 1.05.

FIG. 2(D) is a typical view of an oxidation system in a fourthembodiment according to the present invention. The oxidation system inthe fourth embodiment is provided with an oxidizing gas jetting nozzle90 similar to the oxidizing gas jetting nozzle 64 of the oxidationsystem in the first embodiment shown in FIG. 2(A) and two reducing gasjetting nozzles, namely, a first reducing gas jetting nozzle 92 and asecond reducing gas jetting nozzle 94. The first reducing gas jettingnozzle 92 extends, similarly to the reducing gas jetting nozzle 66 ofthe oxidation system in the first embodiment shown in FIG. 2(A), alongthe wafer boat 8. The first reducing gas jetting nozzle 92 is providedwith a plurality of gas outlets 92 a longitudinally arranged atpredetermined pitches to jet the reducing gas horizontally all over theprocessing space S.

The second reducing gas jetting nozzle 94 is similar to the reducing gasjetting nozzle 88 shown in FIG. 2(C). The second reducing gas jettingnozzle 94 has an up section extending from the upstream region S1 to thedownstream region S3 of the processing space S, a bend formed by bendingthe reducing gas nozzle in the downstream region S3, and a down sectionextending down from the bend to the upstream region S1. The down sectionof the reducing gas jetting nozzle 94 is provided with a plurality ofgas outlets 94A longitudinally arrangement at predetermined pitchessimilarly to the gas outlets 88A of the reducing gas jetting nozzle 88shown in FIG. 2(C).

Generally, when a gas is jetted through a plurality of gas outletsformed in a longitudinal arrangement in a long gas jetting nozzle, thegas is jetted at higher jetting rates through the gas outlets at upperpositions with respect to the flowing direction of the gas in the gasjetting nozzle. Since the oxidation system in the fourth embodiment isprovided with the two long reducing gas jetting nozzles 92 and 94, andthe gas flows through the first reducing gas jetting nozzle 92 upwardand flows through the second section of the second reducing gas jettingnozzle 94 downward, H₂ can be jetted uniformly all over the processingspace S. Films formed by the oxidation system in the fourth embodimenthad a high interfilm thickness uniformity of ±1.5% and satisfactoryintrafilm thickness uniformities within ±1%.

FIG. 2(E) is a typical view of an oxidation system in a fifth embodimentaccording to the present invention. The oxidation system in the fifthembodiment is provided with an oxidizing gas jetting nozzle 96 and areducing gas jetting nozzle 98 respectively corresponding to thereducing gas jetting nozzle 66 and the oxidizing gas jetting nozzle 64.The oxidizing gas jetting nozzle 96 is provided, similarly to thereducing gas jetting nozzle 66 of the oxidation system in the firstembodiment shown in FIG. 2(A), with gas outlets 96A arranged at equalpitches. The reducing gas jetting nozzle 98 has, similarly to theoxidizing gas jetting nozzle 64 of the oxidation system in the firstembodiment, a gas outlet 98A in its free end.

Films formed by the oxidation system in the fifth embodiment had a highinterfilm thickness uniformity of ±1.87%. However, the films formed bythe oxidation system in the fifth embodiment had considerably lowintrafilm thickness uniformities within ±2.58% as compared with those ofthe films formed by the oxidation systems in the first to the fourthembodiment.

Although the oxidation systems embodying the present invention have beendescribed on an assumption that all the gas outlets of the gas jettingnozzles have the same diameter, those gas outlets may have differentdiameters. For example, when a plurality of gas outlets are formed in alongitudinal arrangement in a gas jetting nozzle, the lower gas outletswith respect to the flowing direction of the gas may be formed ingreater diameters in order that the gas is jetted through the gasoutlets at substantially the same jetting rate.

The oxidizing gas is not limited to O₂ and may be N₂O, NO or NO₂. Thereducing gas is not limited to H₂ and may be NH₃, CH₄ or HCl.

The present invention is applicable not only to processing semiconductorwafers but also to processing LCD substrates and glass substrates.

1. An oxidation method comprising the steps of: supplying an oxidizinggas and a reducing gas into a processing vessel defining a processingspace, and capable of holding a plurality of workpieces at predeterminedpitches and of being evacuated; creating a process atmosphere containingactive oxygen species and active hydroxyl species through theinteraction of the oxidizing gas and the reducing gas; and oxidizingsurfaces of the workpieces in the process atmosphere, wherein at leasteither of the oxidizing gas and the reducing gas is supplied by a gassupply nozzle having gas outlets arranged longitudinally and said atleast either of the oxidizing gas and the reducing gas is jetted into anupstream region from the gas outlets disposed at a bottom area of theprocessing space, jetted into a middle region from the gas outletsdisposed at a middle area of the processing space and jetted into adownstream region from the gas outlets disposed at a top area of theprocessing space where the workpieces are held.
 2. The oxidation methodaccording to claim 1, wherein the oxidizing gas is jetted only in theupstream region, with respect to the flowing direction of the gases, ofthe processing space.
 3. The oxidation method according to claim 1,wherein the oxidizing gas contains at least one of O₂, N₂O, NO, NO₂ andO₃, and the reducing gas contains at least one of H₂, NH₃, CH₄, HCl andheavy hydrogen.
 4. The oxidation method according to claim 2, whereinthe oxidizing gas contains at least one of O₂, N₂O, NO, NO₂ and O₃, andthe reducing gas contains at least one of H₂, NH₃, CH₄, HCl and heavyhydrogen.